Video streaming over data networks

Abstract

A client device receives streamed encoded content data, such as encoded video data, which has been encoded at a constant perceptual quality. Several different versions of the content are available to be streamed to the device, at different perceptual quality levels. In order to decide which quality level to request from a content server at intervals the device calculates the delivery rates that would be required for each level of quality. The delivery rates are calculated in dependence on so-called critical points, which are points at which a piecewise constant bit rate delivery schedule is just equal to the decoding schedule. There are two classes of critical points, being a first class of critical points, referred to herein as “additional critical points”, which are points on the decoding schedule where, for any particular other point on the decoding schedule before an additional critical point, and assuming that a minimum threshold amount of data is buffered when delivery occurs from the particular point, a constant bit rate delivery schedule that is calculated for the particular point taking into account the buffered minimum amount of data and of such a rate such that buffer underflow does not occur is substantially equal to the decoding schedule. A second class of critical points, referred to herein as “downstairs critical points”, is also defined, which are derived from the decoding schedule as a whole, and which are the points at which a piecewise monotonically decreasing constant bit rate delivery schedule (the so-called “downstairs” schedule), which is calculated such that when delivering the encoded content data from the start buffer underflow does not occur, is substantially equal to the decoding schedule of the encoded content data. When the actual delivery rate received is ahead of the so-called “downstairs” schedule, then the delivery rate required for a particular quality level can be calculated from the second class of critical points. However, when the actual delivery rate received is behind the downstairs schedule, then the delivery rate required is calculated from the first class of critical points.

Description

TECHNICAL FIELD[0001]The present invention relates to a method and system for the determination of data transfer rate required for the streaming of variable bit rate encoded video data over a network. In some embodiments the determined data transfer rates are then used to select a video quality to be provided over the network for reproduction.BACKGROUND TO THE INVENTION[0002]Traditionally a video on demand service, such as that provided commercially in the UK under the trade name BT Vision, is supported by encoding video at a constant bit rate and delivering it over a network at the same constant bit rate. This generally requires bandwidth reservation on the network, which can be expensive to provide. Video encoded using compression techniques naturally has variable bit rate, as the number of bits produced when encoding a picture depends on the picture content: how similar it is to previously encoded pictures and how much detail it contains. Some video scenes can be coded to a given...

AI Technical Summary

Benefits of technology

The patent describes a method for delivering encoded content data over a network, such as video data, at different quality levels. The method involves determining the data rates required to deliver the content at each quality level and selecting the quality level with the highest data rate. The method takes into account the delivery requirements of the content server and the buffer underflow. By calculating the data rate required for delivery of remaining content based on critical points in the decoding schedule, the method ensures efficient delivery of the content data. The invention also provides pre-calculated data and meta-data related to the content data.

Problems solved by technology

This generally requires bandwidth reservation on the network, which can be expensive to provide.

Also, by fixing the bit rate independent of the genre of the video content, some genres of content can be encoded well, such as news and drama, whereas others, such as fast moving sport and music videos and concerts, can only be coded quite poorly.

However, due to the variability of instantaneous bit rate of VBR encoded data, delivery of variable bit rate encoded data over a network can itself be problematic, if the network is to deliver the data sufficiently quickly such that all video data is delivered in time for it to be decoded and displayed without interruption.

In particular, parts of the VBR encoded data which have a high number of bits per frame, such as action sequences or the like, may lead to high instantaneous data rate requirements which the network is unable to deliver.

Such situations may then lead to buffer underflow at the decoding client, and hence interruptions in delivery.

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